I returned to a browser window on a question I recently answered, and the behavior was really weird. I had the old-school orange notification bar at the top of the window, which said a new answer had been posted, and also saw multiple inline banner notifications (one said a new answer had been posted, another was on a question that had been edited). I clicked on the orange notification, the screen refreshed, and this is what I see (sorry it's huge). Note that David's answer (and my comment to his answer) appears twice.
I am using Chrome 20.0.1132.47 on Max OS X 10.7.4.
I am sure this is some freak collision and entirely not reproducible, and of course when I refresh the page the extra answer has disappeared. But thought I would document it here in case anyone else has seen this or knows why that orange bar (which I haven't seen for ages) would suddenly appear - it must be related.